Dampening Apparatus and Method for Single Piston Pump Used in Determining the Thermal Stability of Fluids

ABSTRACT

A thermal oxidation tester is shown for determining thermal stability of a fluid, particularly hydrocarbons when subjected to elevated temperatures. The tendency of the heated fluid to oxidize and (1) form deposits on a surface of a heater tube and (2) form solids therein, are both measured at a given flow rate, temperature and time. The measured results are used to determine whether a fluid sample passes or fails the test. Results of the measurements are recorded. The fluid under test is pumped with a low volume, high pressure, single piston pump with only a small fluctuation (pulsation) in output flow.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. patent application Ser. No.12/838,104, filed Jul. 16, 2010.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to methods and devices for measuring the thermalcharacteristics of fluids. Specifically, this invention relates to thedampening apparatus and method for a single piston pump used in a systemto measure the thermal oxidation tendencies of fuels for liquidhydrocarbon-burning engines.

2. Background Art

When engines were developed for use in jet aircraft, problems began todevelop for jet fuel due to poor fuel thermal stability. At highertemperatures, the jet fuels would oxidize and form deposits that wouldclog fuel nozzles and fuel filters. These deposits would also collect inthe jet engine.

While various tests were devised and used in the 1950s and 60s to ratethe thermal oxidation characteristics of jet fuels prior to being usedin jet aircraft, Alf Hundere developed the apparatus and method whichbecame the standard in the industry. In 1970, Alf Hundere filed whatbecame U.S. Pat. No. 3,670,561, titled “Apparatus for Determining theThermal Stability of Fluids”. This patent was adopted in 1973 as ASTMD3241 Standard, entitled “Standard Test Method for Thermal OxidationStability of Aviation Turbine Fuels”, also known as the “JFTOT®Procedure”. This early Hundere patent was designed to test thedeposition characteristics of jet fuels by determining (1) deposits onthe surface of a heater tube at an elevated temperature and (2)differential pressure across a filter due to collection of particulatematter. To this day, according to ASTM D3241, the two criticalmeasurements are still (1) the deposits collected on a heater tube and(2) differential pressure across the filter due to the collection ofparticulate matter on the filter.

According to ASTM D3241, 450 mL of fuel flows across an aluminum heatertube at a specified rate, during a 2.5 hour test period at an elevatedtemperature. Currently six different models of JFTOT®¹ instruments areapproved for use in the ASTM D3241-09 Standard. The “09” refers to thecurrent revision of the ASTM D3241 Standard. 1 JFTOT is the registeredtrademark of Petroleum Analyzer Company, LP.

While over the years various improvements have been made in theapparatus to run the tests, the basic test remains the same.Improvements in the apparatus can be seen in U.S. Pat. Nos. 5,337,599and 5,101,658. The current model being sold is the JFTOT 230 Mark III,which is described in further detail in the “Jet Fuel Thermal OxidationTester—User's Manual”. The determination of the deposits that occur onthe heater tube can be made visually by comparing to known colorstandards or can be made using a “Video Tube Deposit Rater” sold underthe Alcor mark.

The determination of the amount of deposits formed on the heater tube atan elevated temperature is an important part of the test. The currentASTM D3241 test method requires a visual comparison between the heatertube deposits and known color standard. However, this involves asubjective evaluation with the human eye. To take away the subjectivityof a person, an electronic video tube deposit rater was developed.

Also, there has been considerable discussion as to the polish or finishof the heater tube. (See U.S. Pat. No. 7,093,481 and U.S. PatentApplication Publication No. US 2002/083,760.) The finish of the heatertube is very important in determining the amount of fuel deposits thatwill form thereon. Therefore, it is important that the quality of thefinish on heater tubes made today be consistent with the finish ofheater tubes made since 1973.

Once the thermal oxidation stability test has been performed on a batchof fuel, the recorded information and the heater tube are preserved toshow the batch of fuel was properly tested. The information that wasrecorded when testing a batch of fuel is maintained separately from theheater tube itself. This can cause a problem if one or the other getsmisplaced or lost. Inaccurate information and/or conclusions occur ifthe wrong set of data is associated with the wrong heater tube.

In prior versions of the JFTOT, a low volume, high pressure pump hasbeen used that has two pistons. A less expensive single piston pumpcaused too large of a variation in output pressure to be used,especially when pumping at such a low volume and high pressure.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus andmethod for testing thermal oxidation stability of fluids, particularlyaviation fuels.

It is another object of the present invention to provide an apparatusand method to measure the tendency of fuels to form deposits when incontact with heated surfaces.

It is another objective of the present invention to provide an apparatusand method for testing the thermal oxidation tendency of fuels utilizinga test sample to determine if solid particles will form in the fuel atan elevated temperature and pressure.

It is another objective of the present invention to provide an apparatusand method for determining thermal oxidation stability of a batch ofaviation fuel by testing a sample at an elevated temperature andpressure to determine (1) deposits that form on a metal surface and (2)solid particles that form in the fuel.

It is another objective of the present invention to provide an apparatusand method for recording and storing the thermal oxidation tendency dataof fuels in single location.

It is yet another objective of the present invention to provide anintelligent heater tube on which a thermal oxidation stability test isperformed with deposits collecting thereon and a memory device on oneend of the intelligent heater tube to record all of the testinformation.

It is another objective of the present invention to have an intelligentheater tube with a memory device on one end thereon on which all of thetest information in association with that heater tube can be recorded.

It is another object of the present invention to provide a memory devicefor an intelligent heater tube that has a ground and data connectionwith the memory device being connected to the heater tube.

It is another object of the present invention to provide an apparatusand method for testing thermal oxidation tendencies of high performancefuels with the test results being written into a memory device on anintelligent heater tube.

It is still another object of the present invention to provide dampeningfor a low volume, high pressure, single piston pump so that such a pumpcan be used when testing thermal oxidation stability of fluids,particularly aviation fuels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general block diagram of a thermal oxidation stability testapparatus illustrating flow and electrical controls.

FIGS. 2 and 2A are a more detailed block diagram showing a thermaloxidation test apparatus used to perform ASTM D3241 Standard.

FIG. 3 is a pictorial diagram of the coolant flow for FIGS. 2 and 2A.

FIG. 4 is a pictorial diagram of the airflow in FIGS. 2 and 2A

FIG. 5 is a pictorial diagram showing flow of the test sample in FIGS. 2and 2A.

FIG. 6 is a lengthwise view of an intelligent heater tube.

FIG. 7 is an exploded perspective end view of the intelligent heatertube of FIG. 6, showing the EEPROM in broken lines inside of a memorydevice on the intelligent heater tube.

FIG. 8 is an elevated view of the 1-Wire EEPROM used in the memorydevice of FIG. 7.

FIG. 9 is a pictorial illustration of how to record data on the memorydevice of an intelligent heater tube.

FIG. 10 is a schematic diagram of the writer module used to write on a1-Wire EEPROM.

FIG. 11 is a schematic diagram of a built-in Video Tube Deposit Raterfor use with an intelligent heater tube.

FIG. 12 is a schematic view illustrating use of a low volume, highpressure, single piston pump with sufficient dampening in a thermaloxidation stability tester.

FIG. 13 is a perspective view of the actual pump schematicallyillustrated in FIG. 12.

FIG. 14 is a top view of the actual pump schematically illustrated inFIG. 12.

FIGS. 15( a) and 15(b) are graphs showing variations in flow of thefluid under test.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic block diagram of a thermal oxidation stabilitytester referred to generally by the reference numeral 20. The thermaloxidation stability tester 20 has an embedded computer 21 with a touchscreen 23 for user interface. While many different types of programscould be run, in the preferred embodiment, Applicant is running C++ inthe embedded computer 21. The touch screen 23 displays all of theinformation from the thermal oxidation stability tester 20 that needs tobe conveyed to the user. The user communicates back and forth with theembedded computer 21 through the touch screen 23. If a batch of fuel isto be tested, a test sample is put in the sample delivery system 25.

It is important to the test to make sure the test sample is oxygensaturated through aeration. Therefore, the embedded computer 21 operatesa sample aeration control 31 for a period of time to make sure thesample is fully aerated. The aeration of the sample takes place at thebeginning of the test.

The embedded computer 21 turns on a sample flow control 27, which is apump used to deliver the sample throughout the thermal oxidationstability tester 20. Simultaneous with the sample flow control 27pumping the test sample throughout the system, sample pressure control29 maintains a fixed pressure throughout the system. It is important tomaintain pressure in the system to prevent boiling of the test samplewhen at elevated temperatures. In the present thermal oxidationstability tester 20, the sample is maintained at approximately 500 psiwhen undergoing the thermal oxidation stability test.

Also, the embedded computer 21 controls parameters affecting theintelligent heater tube 33. The test data is recorded to the intelligentheater tube 33 via intelligent heater tube writer 35 from the embeddedcomputer 21. Critical test parameters are recorded on a memory device(as described subsequently) on an end of the intelligent heater tube 33via the intelligent heater tube writer 35. The rating of the depositformed on the intelligent heater tube 33 will be recorded on the memorydevice at a later time.

In performing the thermal oxidation stability test on a test sample, theintelligent heater tube 33 is heated by tube heater control 37. The tubeheater control 37 causes current to flow through the intelligent heatertube 33, which causes it to heat up to the temperature set point.

To prevent the hot intelligent heater tube 33 from heating other partsof the thermal oxidation stability tester 20, bus-bar coolant control 39provides coolant upper and lower bus-bars holding each end of theintelligent heater tube 33. This results in the center section of theintelligent heater tube 33 reaching the prescribed temperature while theends of the intelligent heater tube 33 are maintained at a lowertemperature. This is accomplished by flowing coolant via the bus-barcoolant control 39 across the ends of the intelligent heater tube 33.

The test parameters, such as the dimension of the heater tube, pressureof the test sample or flow rate are fixed by ASTM D3241 However, thecontrol of these parameters are the focus of this invention.

Referring now to FIGS. 2 and 2A in combination, a schematic flow diagramis shown connecting the mechanical and electrical functions. Theembedded computer 21 and the touch screen 23 provide electrical signalsas indicated by the arrows. A test sample is contained in the samplecontainer 41. To make sure the sample and the sample container 41 isfully aerated, an aeration pump 43 is turned ON. The aeration pump 43pumps air through a dryer 45 where the air is dehumidified to removemoisture. From the dryer 45, a percent relative humidify sensor 47determines the humidity level of the pumped air and provides thatinformation to the embedded computer 21. Assuming the percent humidityof the pumped air is sufficiently low, the test procedure will continuepumping air through the flow meter 49 and aeration check valve 50 intothe sample container 41. During aeration, flow meter 49 should recordapproximately 1.5 liters of air per minute. Since the flow meter 49 runsfor approximately six minutes, the aeration pump 43 will spargeapproximately nine liters of air into the test sample. This issufficient time to saturate the test sample with dry air.

Within the sample container 41, a sample temperature measurement 51 istaken and provided to the embedded computer 21. The sample temperaturemeasurement 51 is to ensure that the test sample is between 15°-32° C.If the test sample is outside of this temperature range, results can beimpacted. Therefore, if the test sample is outside this temperaturerange, the embedded computer 21 would not let the test start.

Once the test sample has been aerated and if all the other parametersare within tolerance, then the sample drive pump 53 will turn ON. Thesample drive pump 53 is a single piston HPLC pump, also known as ametering pump. With every stroke of the piston, a fixed volume of thesample is delivered. The speed of the sample drive pump 53 is controlledso that it pumps 3 mL/min of the test sample. The sample drive pump 53is configured for fast refill which minimizes the need for manual pumppriming. Pulsations, associated with pumps of this design are minimizedwith the use of a pulse dampener and a coil tubing on the outlet side aswill be subsequently described.

To get air out of the tubing between the sample container 41 and thesample drive pump 53 at the start of the test, an auto pump primingvalve 55 is opened, a sample vent valve 54 is closed and the aerationpump 43 is turned ON by the embedded computer 21. The auto pump primingvalve 55 opens and remains open while a combination of sample and air isdischarged into waste container 57. At the same time the aeration pump43 provides positive pressure in the sample container 41 to force testsample from the sample container 41 to the sample drive pump 53. Thesample vent valve 54 closes to prevent venting of the air pressure toatmosphere to maintain a pressure of 2 to 3 psi. A sample vent checkvalve 56 across the sample vent valve 54 opens at 5 psi to prevent thepressure in the sample container 41 from exceeding 5 psi. Once thesample drive pump 53 starts pumping the test sample, auto pump primingvalve 55 will close and the sample vent valve 54 will open. Thereafter,the sample drive pump 53 will pump the test sample through check valve59 to the prefilter 61. The check valve 59 prevents fluid from flowingbackwards through the sample drive pump 53. The check valve 59 operatesat a pressure of approximately 5 psi. The check valve 59 preventssiphoning when the sample drive pump 53 is not pumping. Also, checkvalve 59 prevents fluid from being pushed backwards into the sampledrive pump 53.

The pre-filter 61 removes solid particles in the test sample that couldaffect the test. The pre-filter 61 is a very fine filter, normally inthe order of 0.45 micron in size. The purpose of the pre-filter 61 is tomake sure particles do not get into the test filter as will bedescribed. The pre-filter 61 is replaced before every test.

From the pre-filter 61, the test sample flows through an inlet 63 intothe cylindrical heater tube test section 65. Outlet 67, whileillustrated as two separate outlets, is actually a single outlet at theupper end of the cylindrical heater tube test section 65. Extendingthrough the cylindrical heater tube test section 65 is the intelligentheater tube 69, sealed at each end with ceramic bushings and an o-ring(not shown). While the test sample flows through the cylindrical heatertube test section 65 via inlet 63 and outlet 67 and around theintelligent heater tube 69, the housing of the cylindrical heater tubetest section 65 is electrically isolated from the intelligent heatertube 69. Only the test sample comes in contact with the center sectionof the intelligent heater tuber 69. Inside of the intelligent heatertube 69 is a thermocouple 71 that sends a signal back to the embeddedcomputer 21 as to the temperature of the center section of theintelligent heater tube 69.

Test sample flowing from the cylindrical heater tube test section 65flows through a differential pressure filter 73, commonly called the“test filter”. In a manner as will be explained in more detail, theintelligent heater tube 69 heats up the test sample inside of thecylindrical heater tube test section 65 to the test parameter set point.Heating of the test sample may result in degradation of the test sample,or cause solid particles to form. The solid particles may deposit on thecenter section of the intelligent heater tube 69, and/or may collect onthe differential pressure filter 73. The pressure drop across thedifferential pressure filter 73 is measured by differential pressuresensor 75. Pressure across the differential pressure filter 73 iscontinuously monitored by the embedded computer 21 through thedifferential pressure sensor 75. When the pressure across thedifferential pressure filter 73 exceeds a predefined differential ofapproximately 250 mm to 280 mm of mercury, the differential pressurebypass valve 77 opens to relieve the pressure. By test definition,exceeding a differential pressure of 25 mm Hg results in failure of thetest.

For this test to be performed, the test sample must remain as a liquid.At typical testing temperatures of 250° C. to 350° C., many hydrocarbonfuels will transition to the vapor phase at ambient pressures. To keepthe test sample in the liquid phase, the back pressure regulator 79maintains approximately 500 psi pressure in the system. This systempressure is monitored by the system pressure sensor 81, which reportsinformation to the embedded computer 21. During a test, normal flow of atest sample is through differential pressure filter 73 and through theback pressure regulator 79. From the back pressure regulator 79, thetest sample flows through sample flow meter 83 to waste container 57.The sample flow meter 83 accurately measures the flow rate of the testsample during the test. The sample flow meter 83 provides sample flowrate information to the embedded computer 21.

A system/safety vent valve 85 is connected into the system andcontrolled via the embedded computer 21. The system/safety vent valve 85acts to relieve excess system pressure in the case of power loss,improperly functioning system components or other system failures. Inthe event of this occurrence, the system pressure sensor 81 sends asignal to the embedded computer 21, triggering the system/safety ventvalve 85 to open and relieve excess pressure. Also, at the completion ofa test, the system/safety vent valve 85 opens to vent pressure from thesystem. The system/safety vent valve 85 is normally set to the openposition requiring a program command to through the embedded computer 21to close the system/safety vent valve 85. Therefore, if power is lost,the system/safety vent valve 85 automatically opens.

At the end of the test, after the system/safety vent valve 85 is openedand system pressure is relieved, the flush air pump 87 turns ON andflushes air through flush check valve 89 to remove the test sample fromthe system. The flush air pump 87 pushes most of the test sample out ofthe system via the system/safety vent valve 85 into the waste container57.

The system may not operate properly if there are air pockets or airbubbles in the system. During a test, it is important to maintain anair-free system. Therefore, at the beginning of each test, the solenoidoperated differential pressure plus vent valve 91 and the differentialpressure minus vent valve 93 are opened so that the test section 65,differential pressure filter 73, differential pressure sensor 75 andconnecting differential pressure line are, flushed with test sample, andvented to remove any air pockets that may be present. During thebeginning of each test, the position of the differential pressure ventvalves 91 and 93 ensure there is no air in the differential pressurelines.

If the waste container 57 is properly installed in position, a signalwill be fed back to the embedded computer 21 indicating the wastecontainer 57 is correctly connected. This also applies for the samplecontainer 41 which sends a signal to the embedded computer 21 when it isproperly connected. The system will not operate unless both the wastecontainer 57 and the sample container 41 are properly positioned.

The center portion of the intelligent heater tube 69 is heated to thetest parameter set point by flowing current through the intelligentheater tube 69. Instrument power supplied for current generation and allother instrument controls is provided through local available power 95.Depending on local power availability, local available power 95 may varydrastically. In some areas it is 50 cycles/sec. and in other areas it is60 cycles/sec. The voltage range may vary from a high of 240 Volts downto 80 Volts or less. A universal AC/DC converter 97 takes the localavailable power 95 and converts it to 48 Volts DC. With the universalAC/DC converter 97, a good, reliable, constant 48 Volts DC is generated.The 48 Volts DC from the universal AC/DC converter 97 is distributedthroughout the system to components that need power through the DC powerdistribution 99. If some of the components need a voltage level otherthan 48 Volts DC, the DC power distribution 99 will change the 48 VoltsDC to the required voltage level.

To heat the intelligent heater tube 69, the 48 Volts from the universalAC/DC converter 97 is converted to 115 Volts AC through 48 Volt DC/115Volts AC inverter 101. While taking any local available power 95,running it through a universal AC/DC converter 97 and then changing thepower back to 115 Volts AC through DC/AC inverter 101, a stable powersupply is created. While this design uses 48 Volts DC, it is possible touse a universal AC/DC converter and DC/AC inverter that operates withother voltages such as 12 Volts DC, 24 Volts DC or 230 Volts AC. Fromthe 48 Volts DC/115 Volts AC inverter 101, power is supplied to theheater tube module 103. The heater tube module 103 then supplies currentthat flows through the intelligent heater tube 69 via upper clamp 105and lower clamp 107. The heater tube module 103 is controlled by theembedded computer 21 so that during a normal test, the thermocouple 71inside of the intelligent heater tube 69 will indicate when theintelligent heater tube 69 has reached the desired temperature.

While the center section of the intelligent heater tube 69 heats todesired test set point, the ends of the intelligent heater tube 69should be maintained near room temperature. To maintain the ends of theintelligent heater tube 69 near room temperature, a coolant flowsthrough an upper bus-bar 109 and lower bus-bar 111. The coolant insidethe upper bus-bar 109 and lower bus-bar 111 cools the upper clamp 105and lower clamp 107 which are attached to the ends of the intelligentheater tube 69. The preferred cooling solution is a mixture ofapproximately 50% water and 50% antifreeze (ethylene glycol). As thecoolant flows through electrically non-conductive conduit 135 to thecoolant container 115, the flow is measured by flow meter 113. Tocirculate the coolant, a cooling pump 117 pumps the coolant solutioninto a radiator assembly 119. Inside of the radiator assembly 119, thecoolant is maintained at room temperature. The radiator fan 121 helpsremove heat from the coolant by drawing air through the radiatorassembly 119. From the radiator assembly 119, the coolant flows throughelectrically non-conductive conduit 131 into the lower bus-bar 111 thenthrough electrically non-conductive conduit 108 to upper bus-bar 109prior to returning via the flow meter 113.

The flow meter 113 is adjustable so that it can ensure a flow ofapproximately 10 gal./hr. The check valve 123 helps ensure the coolingsystem will not be over pressurized. Check valve 123 will open at around7 psi, but normally 3-4 psi will be developed when running the coolantthrough the entire system.

To determine if the intelligent heater tube 69 is shorted to the testsection housing (65 in FIG. 2), a heater tube short detector 110monitors a short condition. If a short is detected, the embeddedcomputer 21 is notified and the test is stopped.

On one end of the intelligent heater tube 69 there is a memory device125 to which information concerning the test can be recorded by IHTwriter 127 as will be discussed in more detail. While a test is beingrun on a test sample, the IHT writer 127 will record information intothe memory device 125. At the end of the test, all electronicinformation will be recorded onto the memory device 125 of theintelligent heater tube 69, except for the manual tube deposit rating.To record this information, the intelligent heater tube 69 will have tobe moved to another location to record the deposit rating either (a)visually or (b) through a Video Tube Deposit Rater. At that time, asecond IHT writer will write onto the memory device 125. The Video TubeDeposit Rater may be built into the system or may be a standalone unit.

The intelligent heater tube 69 is approximately 6¾″ long. The ends areapproximately 3/16″ in diameter, but the center portion that is heatedis approximately ⅛″ in diameter. Due to very low electrical resistanceof aluminum, approximately 200 to 250 amps of current flows through theintelligent heater tube 69. Both the voltage and the current through theintelligent heater tube 69 is monitored by the embedded computer 21, butalso the temperature of the center section of the intelligent heatertube 69 is monitored by the thermocouple 71 which is also connected tothe embedded computer 21. The objective is to have the center section ofthe intelligent heater tube 69 at the required temperature. To generatethat type of stable temperature, a stable source of power is providedthrough the universal AC/DC converter 97 and then the 48 VDC/115 VACinverter 101. By using such a stable source of power, the temperature onthe center section of the heater tube 69 can be controlled within acouple of degrees of the required temperature even if the localavailable power is unstable.

Referring now to FIG. 3 of the drawings, a pictorial representation ofthe coolant flow during a test is illustrated. Like numbers will be usedto designate similar components as previously described. A pictorialillustration of the heater tube test section 129 is illustrated on thelower left portion of FIG. 3. Coolant from the radiator assembly 119 isprovided to the lower bus-bar 111 via conduit 131 then to upper bus-bar109 via conduit 108. From the upper bus-bar 109, the coolant flows viaconduit 133 to flow meter 113. From flow meter 113, the coolant flowsthrough conduit 135 to the coolant container 115. The cooling pump 117receives the coolant through conduit 137 from the coolant container 115and pumps the coolant into radiator assembly 119. If the pressure fromthe cooling pump 117 is too high, check valve 123 will allow some of thecoolant to recirculate around the cooling pump 117. FIG. 3 is intendedto be a pictorial representation illustrating how the coolant flowsduring a test.

Likewise, FIG. 4 is a pictorial representation of the aeration systemfor the test sample. Similar numbers will be used to designate likecomponents as previously described. An aeration pump 43 pumps airthrough conduit 139 to a dryer 45. The dryer 45 removes moisture fromthe air to prevent the moisture from contaminating the test sampleduring aeration. From the dryer 45, the dried air will flow throughconduit 141 to humidity sensor 47. If the percent relative humidity ofthe dried air blowing through conduit 141 exceeds a predetermined amountof 20% relative humidity, the system will shut down. While differenttypes of dryers 45 can be used, it was found that Dry-Rite silica geldesiccant is an effective material for producing the desired relativehumidity.

From the percent humidity sensor 47, the dried air flows through conduit143 to flow meter 49, which measures the air flow through conduit 143and air supply conduit 145. From air supply conduit 145, the dried airflows through aeration check valve 50 and conduit 146 sample containerarm mounting clamp 147 and sample container arm 149 to aeration conduit151 located inside of sample container 41. In the bottom of samplecontainer 141, a glass frit 153 connects to aeration conduit 151 tocause the dried air to sparge through the test sample in samplecontainer 41. When the sample container 41 is in place and the samplecontainer arm 149 is connected to the sample container arm mounted clamp47, contact 155 sends a signal to the embedded computer 21 (see FIG. 2)indicating the sample container 41 is properly installed.

Referring now to FIG. 5, a pictorial illustration of the flow of thetest sample in connection with FIGS. 2 and 2A is shown in a schematicflow diagram. The test sample is contained in sample container 41, whichis connected via sample container arm 149 to the sample container armmounting clamp 147. Vapors given off by the test sample are dischargedthrough a vent 157, normally through a vent hood to atmosphere.Simultaneously, the sample drive pump 53 draws some of the test sampleout of the sample container 41. The sample drive pump 53 is a singlestroke HPLC pump connected to a pulse dampener. While the pulse dampener159 may be configured a number of ways, the pulse dampener 159 in thepreferred configuration has a diaphragm with a semi-compressible fluidon one side of the diaphragm. This fluid is more compressible than thetest sample thereby reducing pressure changes on the test sample flowdischarged from the sample drive pump 53. The sample drive pump 53 isconnected to auto pump priming valve 55. During start-up, the closedauto pump priming valve 55 opens until all of the air contained in thepump and the lines are discharged into the waste container 57. In caseit is needed, a manual priming valve 161 is also provided. Additionally,the aeration pump 43 is turned ON to provide a slight pressure in thesample container 41 of about 2 to 3 psi. The sample vent valve 54 closesto prevent this pressure escaping to atmosphere. This pressure will helppush the fluid sample from the sample container 41 to the inlet of thesample drive pump 53. The 5 psi check valve 56 prevents the pressure inthe sample container exceeding 5 psi. During the test, coil 163 alsoprovides further dampening in addition to the pulse dampener 159. Checkvalve 59 ensures there is no back flow of the sample fuel to the sampledrive pump 53. However, at the end of a test, flush check valve 89receives air from flush air pump 87 to flush the test sample out of thesystem.

During normal operation of a test, the sample fuel will flow throughcheck valve 59 and through a pre-filter 61 removing most solidparticles. Following the pre-filter 61, the test sample flows into theheater tube test section 129 and then through the differential pressurefilter 73. Each side of the differential pressure filter 73 connects tothe differential pressure sensor 75. Also connected to the differentialpressure filter 73 is the back pressure regulator 79. The pressure onthe system is continuously monitored through the system pressuretransducer 81. If for any reason pressure on the system needs to bereleased, system/safety vent valve 85 is de-energized and thepressurized test sample is vented through the four-way cross connection165 to the waste container 57.

At the beginning of the test, to ensure there is no air contained in thesystem, the differential pressure plus vent valve 91 and thedifferential pressure minus vent valve 93 are opened to vent anypressurized fluid through the four-way cross connection 165 to the wastecontainer 57.

In case the differential pressure filter 73 clogs so that thedifferential pressure exceeds a predetermined value, differentialpressure bypass valve 77 will open to relieve the pressure.

To determine the exact flow rate of the test sample through the system,the sample flow meter 83 measures the flow rate of test sample from theback pressure regulator 79 before being discharged through the wastecontainer arm 167 and the waste container clamp 169 into the wastecontainer 57. The waste container 57 is vented all the time through vent171.

Intelligent Heater Tube (IHT)

The intelligent heater tube (IHT) 69 is shown in FIG. 6. The intelligentheater tube 69 is cylindrical in shape as described previously. The top173 and bottom 175 are 3/16″ in diameter. The test section 177 is ⅛″ indiameter. Extending longitudinally along the center axis of theintelligent heater tube 69 is a center bore 179. The thermocouple 71(previously described in conjunction with FIG. 2A) is located inside thecenter bore 179. At the end of the enlarged bottom 175 is a memorydevice 125. The memory device 125 is slightly smaller in diameter thanthe heater tube bottom 175.

As shown in FIGS. 7 and 8 in combination with FIG. 6, an EEPROM 181 islocated inside of the memory device 125. The EEPROM 181 only has a datasignal and a ground signal. The ground signal connects to ground stick183 and the data signal connects to data plate 185. The ground stick 183fits inside of the center bore 179 of the intelligent heater tube 69.The EEPROM 181 is contained inside of insulated housing 187 of thememory device 125. The data plate 185 is on the end of the insulatedhousing 187 and is slightly smaller in diameter than the insulatedhousing 187. The only two connections to the memory device 125 arethrough the ground stick 183 and the data plate 185.

While the EEPROM 181 has a total of six solder connections 189, only twoof them are connected to either the ground stick 183 or data plate 185.The data plate 185 is made from a material that will not tarnish easilysuch as phosphorous bronze or beryllium copper. The entire memory device125 is resistant to degradation from jet fuel or related materials. Toensure there is no accidental electrical connection, the data plate 185is slightly smaller in diameter than the insulated housing 187 of memorydevice 125, which in turn is slightly smaller in diameter than theenlarged bottom 175 of the intelligent heater tube 69.

Referring to FIG. 9, a pictorial example of how to connect to the memorydevice 125 of the intelligent heater tube 69 when running a test of asample fuel is shown. The intelligent heater tube 69 is held in positionby lower clamp 107. The ground stick 183 of the EEPROM 181 is containedinside of center bore 179 of the enlarged bottom 175.

To write to and from the EEPROM 181, an IHT writer 127 as shown inconnection with FIG. 2A is used. The IHT writer 127 has a data line thatconnects to a spring-loaded contact 191 that pushes against, and makeselectrical contact with, the data plate 185. The other side of the IHTwriter 127 connects to ground via lower clamp 107, intelligent heatertube 69 and ground stick 183. The output from the IHT writer 127 caneither go directly to the JFTOT®, to a video tube deposit rater, or to apersonal computer. Normally, there will be two IHT writers 127. One IHTwriter 127 will be located inside of a jet fuel thermal oxidationstability tester (JFTOT®). Another IHT writer 127 will be used to recordthe deposit information as collected on the test section 177 of theintelligent heater tube 69 as is recorded either (a) manually from avisual inspection or (b) with the Video Tube Deposit Rater. The IHTwriter 127 when installed on the test apparatus only communicates withthe embedded computer 21 shown in FIG. 2. After the test has been run,the only information lacking on the memory device 125 is recording theheater tube deposit rating. This will be recorded either from a manualinspection of the intelligent heater tube 69 or from a video tubedeposit rater, either of which will require a separate IHT writer module127.

Referring now to FIG. 10, the IHT writer module 127 is shown in moredetail. The IHT writer module 127 uses 5 Volts DC as its normal power. AUSB port 193 is used to connect the IHT writer 127. USB port 193 hasfour wires for a positive supply voltage VCC, a negative signal voltageD−, a positive signal voltage D+ and a ground GND. Also, the IHT writer127 has a RS 232 port with four wires being used to transmit data TXD,received data RXD, ground GND, and positive supply voltage VCC. From theIHT writer 127, one wire is for data and one wire is for ground whichare used when connecting to the memory device 125 containing the EEPROM181. The USB port 193 and the RS 232 port 195 supplies data through theIHT writer 127 to the memory device 125. Inside of the IHT writer 127 isa UART TTL level 197 that converts the data to the appropriate form tocommunicate to EEPROM 181. The abbreviation UART stands for “UniversalAcrosynchronous Receiver/Transmitter”. TTL is an abbreviation for“Transistor-Transistor Logic”.

The JFTOT® 230 Mark III can be configured with or without a Video TubeDeposit Rater, to work with the intelligent heater tube 69 having thememory device 125 as shown in the combination of FIGS. 10 and 11. Theembedded computer 21 connects through RS 232 port 195 to the secondintelligent heater tube writer 201, which is similar to IHT writer 127.If the test system does not have a video tube deposit rater module, thenIHT writer 203 may be used to write to the memory device 125 of theintelligent heater tube 69. In this manner, the IHT writer 203 can beused to manually input the data into the memory device 125.

On the other hand, if the testing apparatus does have a Video TubeDeposit Rater, RS 232 port 196 connects the embedded computer 21 to theVideo Tube Deposit Rater (VTDR) module 205. By pressing the eject/closedevice 207, the door of the VTDR module 205 will open and theintelligent heater tube 69 may be inserted. By pushing the start button209, deposits collected on the intelligent heater tube 69 during thetest are rated. The rating is automatically recorded onto the EEPROMchip 181 (not shown in FIG. 11) contained in the memory device 125.

Also, the image data from the VTDR module 205 may be retrieved by VTDRLAN connection 211.

It is important to remember that two different IHT writer modules areused in the full system. One writer module is used while the heater tubeis in the run position. The other writer module is used when the depositrating is being recorded.

After the information has been recorded on the memory device 125,eject/close device 207 is pressed to open the door to allow removal ofthe intelligent heater tube 69. Now, all of the information recordedfrom that test is contained with the intelligent heater tube 69. Sincemost users keep the recorded data and the heater tube, this allows bothto be archived together.

Sample Drive Pump

The sample drive pump as shown in FIGS. 2 and 5 is a high-pressure,low-volume pump. Prior versions of the JFTOT that have been available onthe market use a dual-piston pump to prevent wide swings in pump outletsample flow during strokes of the piston. However, one of the drawbacksof using a dual-piston pump occurs after long periods of non-use whereremnants of a test sample can dry and leave a sticky residue on thecheck valve. Sticky check valves can make it difficult to prime the pumpbecause once the check valves for one of the pistons becomes operationalit has a tendency to allow sample to flow through the now flowing valvesand bypass the other stuck check valves. This will require the need todisassemble the piston and clean the check valves. However, asingle-piston pump has only one path for sample flow that has to beprimed for use. The sample drive pump 53 of the present invention is asingle piston pump, but with numerous ways to prevent fluctuations inoutput flow between strokes of the single piston. The sample drive pump53 is operated by a control module 300 as shown in the schematic of FIG.12. The control module 300 receives its power from DC power distribution99 shown in FIG. 2A. Also, the control module 300 is connected to theembedded computer 21. The embedded computer 21 is operated by touchscreen 23. Control module 300 communicates with the embedded computer 21through communications line 302. Enable line 304 allows the embeddedcomputer 21 to turn the sample drive pump 53 ON or OFF through controlmodule 300.

Also, the embedded computer 21 has an ON/OFF signal 306 to the DC powerdistribution 99, which ON/OFF signal 306 will turn power ON or OFF tothe sample drive pump 53 via control module 300. Therefore, if theembedded computer 21 determines that any part of the JFTOT is notoperating properly, including the program, power thereto can be shutOFF. Turning power OFF to the sample drive pump 53 is a safety mechanismin case something is not operating properly.

From the DC power distribution 99, the +48 Volts being supplied throughthe control module 300 is used to provide motor power 310 to motor 308.Also, DC power distribution 99 provides +21 Volts to operate theelectronics contained in the control module 300.

The motor 308 is a stepper motor that will turn incrementally pursuantto pulses received from the control module 300 in the form of motorpower 310. By incrementally providing power to motor 308, the motor 308will incrementally turn, which incrementally turns drive belt 312. Thedrive belt 312 has teeth therein that mates with a tooth gear (notshown) so there is no slippage between the drive belt 312 and the toothgear. A tooth gear is provided on both ends of the drive belt 312 aswill be explained in detail subsequently.

As the drive belt 312 turns, eccentric cam 314 also turns. Eccentric cam314 is an off-centered cam with an eccentric shape that rotates in acircle about center as pictorially illustrated. By use of the eccentriccam 314, shaft 322 is pushed during 270° of rotation of the eccentriccam 314, and retracted during only 90° of rotation of eccentric cam 314.A spring (not shown in FIG. 12) continually urges the shaft 322 againstthe eccentric cam 314. The eccentric cam 314 and shaft 322 are heldtogether by mechanical assembly 324.

Also, as eccentric cam 314 turns, slotted disc 316 also turns at thesame rotational speed or a rotational speed directly proportionalthereto. By having a slot 317 in the slotted disc 316, anopto-interrupter 318 can sense when the slot 317 passes adjacent theretoand sends a pulse signal 320 to the control module 300. The pulse signal320 lets the control module 300 know that the motor 308 is running,eccentric cam 314 turning and at what speeds.

As the shaft 322 contained inside of mechanical assembly 324 moves backand forth (i.e., left and right) while pressing against eccentric cam314, shaft 322 moves piston 326 back and forth inside of pump head 328.Pump head 328 is receiving fuel from the sample container 41 throughcheck valve 332. As piston 326 retracts from pump head 328, a seal 330prevents leakage around piston 326. Therefore, since check valve 332 isa gravity-operated ball-and-seat check valve, retraction of the piston326 from the pump head 328 will draw fluid from the sample container 41,through check valve 332, into the pump head 328. When the piston 326extends into the pump head 328, pressure is increased in pump head 328which closes check valve 332 and opens check valve 334. Check valve 334,is also a gravity-operated ball-and-seat check valve. While manydifferent types of check valves can be used, a gravity-operated checkvalve with a large seat area helps prevent sticking after periods ofnon-use. During non-use, remnants of a test sample may have remainedtherein, dried up and left a sticky coating, so using a check valve witha large ball and seat provides a larger area to help any pressure acrossthe valve to unstick the valve.

Pressure inside of the pump head 328 of the sample drive pump 53 isanywhere from 500 to 2,500 psi, depending upon the flow rate. In normaloperations over 1,000 psi will be seen in the pump head 328. Any gas orair contained inside of pump head 328 will cause the sample drive pump53 to not operate properly so it is important to remove any air duringpriming.

By having the eccentric cam 314, piston 326 extends into the pump head328 during three-fourths (or 270°), of each rotation of motor 328 andeccentric cam 314. However, the speed of the motor can be increased ordecreased by changing the pulses that are being feed thereto from thecontrol module 300. By increasing the frequency of the steps and hencespeed of motor 308 during the 90° of rotation when the piston 326 isbeing retracted, the lag time between pumping cycles is decreased. Byincreasing the frequency of the pulses to motor 308 when piston 326 isbeing retracted from the pump head 328, the motor can be made to operatefour times faster when retracting piston 326. Therefore, by thecombination of the eccentric cam 314 and the speeding up of the motor308 when retracting piston 326, the pump head 328 can be pumpingapproximately 94% of the time and only spend 6% of the time retracting.This greatly reduces the time of flow pulsations in test fluid beingdischarged through outlet check valve 334. However, the flow pulsationssent from pump head 328 is further reduced by pulse dampener 159. Pulsedampener 159 receives the pressurized test sample from pressure conduit342 connected to outlet check valve 334. The pulse dampener 159 has adiaphragm therein (not shown) which has a semi-compressible fluid on oneside thereof and the pressurized test sample on the other side. In thepresent invention, the semi-compressible fluid is alcohol. Therefore, aseach pulsation of pressurized test sample is received from check valve334, pulse dampener 159 acts to smooth out the sample flow fluctuationsor pulses.

To further provide dampening of the flow pulses of the pressurized testsample, a restriction is added downstream of the pulse dampener 159 inthe form of a 500 psi coil 163. At a flow rate of 3 ml./min., the 500psi coil 163 will cause a pressure drop of 500 psi. In the preferredembodiment the coil 163 has a 1/16″ outside diameter and is made fromstainless steel tubing. The inside diameter is 7/1,000 of an inch. Inthe coil 163, there are approximately four loops about 4″ in diameter.The inlet pressure to coil 163 will be approximately 1,000 psi and theoutlet pressure approximately 500 psi with a flow rate of 3 ml./min.there through. The pressurized test sample from coil 163 feeds throughcheck valve 59 (see FIG. 2) into the entire system for testing todetermine the thermal stability of the fluid under test. While differentconfigurations of quantities of pulse dampeners, sizes of pressure coilsand check valve sizes can be used, the components described in thisembodiment provide the same flow pulsations as the dual-piston pump usedin the previous versions of the JFTOT.

To make sure there is no blockage and that everything is operatingproperly, pulse dampener 159 has a pressure transducer 336 that providesa pressure signal 338 back to the control module 300. In that matter,the control module 300 can monitor the outlet pressure by the pulsedampener 159 to make sure the pressure is not too high. If the pressuregets too high, the control module 300 can stop motor 308 and stop thetest. The control module 300 can further send a signal to notify theembedded computer 21 that the pump has stopped. The embedded computer 21then turns OFF the remaining parts of the JFTOT. Feedback throughpressure transducer 336 is an additional safety feature to ensure thateverything is operating properly.

Referring now to FIGS. 13 and 14 in combination, the mechanical layoutof the sample drive pump 53 is shown. Everything for the sample drivepump 53 is mounted on base 344. Base 344 has bracket 345 supporting thecontrol module 300 thereon. Heat sink 348 helps dissipate any heatgenerated by the electronics contained in the control module 300.

Also, the mechanical assembly 324 is attached to base 344 by legs 347that are secured to the base 344 and rest against vibration dampeners346. While the leg 347 can be made in many different ways, legs 347 areformed integrally with the mechanical assembly 324.

As the control module 300 turns on the motor 308, belt drive 312 beginsto turn. Drive sprocket 311 has teeth therein to match the tooth portionof the belt drive 312. Likewise, cam sprocket 313 has sprockets thereinto match the belt drive 312. This ensures the belt drive 312 will notslip on either the drive sprocket 311 or cam sprocket 313.

As the eccentric cam 314 turns, it pushes against shaft 322, which isurged against eccentric cam 314 by spring 323. As the shaft 322 ispushed forward, it pushes piston 326 forward into pump head 328.Likewise, as shaft 322 retracts, piston 326 will retract from pump head328.

Retraction of the piston 326 from the pump head 328 creates a partialvacuum in pump head 328 causing gravity-operated check valve 332 toopen, which draws part of the test sample from sample container 41 intothe pump head 328. The withdrawing of the piston 326 from the pump head328 only occurs approximately 6% of the time. The remaining 94% of thetime, the piston 326 is being inserted into the pump head 328 whichcreates pressure in pump head 328 that closes check valve 332 and opensoutlet check valve 334. Pressurized test sample flows through outletcheck valve 334 and pressure conduit 342 into pulse dampener 159. Aftersome dampening of the flow fluctuation inside of pulse dampener 159, thepressurized sample flows through flow conduit 350 and T-connection 340into 500 psi coil 163. The coil 163 provides about a 500 psi pressuredrop therein which acts to further dampen the flow fluctuations of thetest sample as it comes out of the pulse dampener 159.

By using the sample drive pump 53 as just described with the singlepiston head, but with (a) an eccentric cam 314, (b) variable speedstepper motor 308, (c) pulse dampener 159 and (d) a restrictive coil163, the variations in flow of the test sample have been minimized.Referring to FIG. 15, FIG. 15( a) shows the overall variation in anormal 3.0 mL/min flow versus time. FIG. 15( b) shows an expanded flowvariation versus time with the lower part of the chart cut off. Thevariation in flow of the test sample when compared to the overall flowof the test sample is insignificant. By use of the techniques as justdescribed, a single piston pump can be used as the sample drive pump 53when testing for thermal stability of fluids, particularly jet fuel.

1. An apparatus for testing thermal oxidation stability of a test samplesuch as a hydrocarbon fuel comprising: a source of electric power; aheater tube connected to said source of electric power for flowingcurrent there through to heat a center section of said heater tube to apredetermined temperature; a coolant flow circuit supplying coolant toeach end of said heater tube to keep each end thereof near roomtemperature; an aeration circuit with an aeration pump for pumping airto aerate said test simple in a sample container; a test sample flowcircuit for flowing said test sample around said center section of saidheater tube to heat said test sample to said predetermined temperature,said test sample flow circuit including: a single piston sample drivepump pumping said test sample from said sample container around saidcenter section of said heater tube; a differential pressure filter insaid test sample flow circuit after said heater tube to filter out anysolids that may have formed in said test sample when heated to saidpredetermined temperature due to oxidation of said test sample; adifferential pressure sensor for measuring differential pressure acrosssaid differential pressure filter; a back pressure regulator formaintaining said test sample being pumped by said sample drive pump at atest pressure high enough to keep said test sample in a liquid phasewhen heated to said predetermined temperature; waste container forcollecting such hydrocarbon fuel after said test; a device for recordingsaid differential pressure and deposits on said center section.
 2. Theapparatus for testing thermal oxidation stability of said test sample asrecited in claim 1 wherein said single piston drive pump is a positivedisplacement pump.
 3. The apparatus for testing thermal oxidationstability of said test sample as recited in claim 2 wherein said singlepiston sample drive pump is driven by a stepper motor with a controlmodule.
 4. The apparatus for testing thermal oxidation stability of saidtest sample as recited in claim 3 wherein output flow from said singlepiston sample drive pump has dampening thereon.
 5. The apparatus fortesting thermal oxidation stability of said test sample as recited inclaim 4 wherein said dampening includes a pulse dampener on an outputside of a pump head of said single piston sample drive pump.
 6. Theapparatus for testing thermal oxidation stability of said test sample asrecited in claim 5 wherein said dampening further includes a restrictiondownstream of said pulse dampener.
 7. The apparatus for testing thermaloxidation stability of said test sample as recited in claim 6 whereinsaid restriction is a high pressure, low flow rate coil.
 8. Theapparatus for testing thermal oxidation stability of said test sample asrecited in claim 5 wherein said pump head has gravity activated checkvalves on an inlet and said outlet side.
 9. The apparatus for testingthermal oxidation stability of said test sample as recited in claim 2wherein said single piston sample drive pump has a motor driving aneccentric cam that provides pumping approximately three times longerduring each cycle than suction.
 10. The apparatus for testing thermaloxidation stability of said test sample as recited in claim 9 where acontrol module speeds up said motor approximate three times fasterduring suction than during pumping.
 11. The apparatus for testingthermal oxidation stability of said test sample as recited in claim 1wherein variations in flow output of said single piston sample drivepump is dampened by (a) an eccentric cam to increasing pumping time, (b)increasing speed of a pumping motor therein during suction, (c) a pulsedampener on an output thereof and (d) a high pressure coil also on saidoutput.
 12. A method of testing a test sample in liquid form for thermaloxidation stability comprising the following steps: aerating said testsample in a sample container with dry air to saturate said test samplewith oxygen; heating a center section of an a heater tube to apredetermined temperature by flowing current there through; cooling eachend of said heater tube by flowing coolant from a coolant flow circuitto said each end; pumping said test sample at a high pressure, low flowrate, around said center section of said heater tube so that temperatureof said test sample is raised to approximately said predeterminedtemperature; test filtering with a differential pressure filter saidtest sample to collect solids formed in said test sample when heated tosaid predetermined temperature; maintaining an elevated pressure on saidtest sample during said pumping step sufficient to keep said test samplefrom evaporating; discharging said test sample to a waste container;recording results from the preceding steps; and dampening said pumpingstep to reduce variation of flow in said elevated pressure of said testsample during testing.
 13. The method of testing the test sample inliquid form for thermal oxidation stability as recited in claim 12wherein said pumping step is with a single piston pump having said highpressure, low flow rate.
 14. The method of testing the test sample inliquid form for thermal oxidation stability as recited in claim 13,wherein said dampening occurs on an outlet of said single piston pump.15. The method of testing the test sample in liquid form for thermaloxidation stability as recited in claim 14 wherein said dampening isprovided by (a) a pulse dampener on said outlet and (b) a restriction onsaid outlet.
 16. The method of testing the test sample in liquid formfor thermal oxidation stability as recited in claim 15 wherein saidrestriction is a high pressure, low flow rate coil.
 17. The method oftesting the test sample in liquid form for thermal oxidation stabilityas recited in claim 12 wherein said pumping step includes a variablespeed motor that is increased in speed during a suction portion of acycle, but decreased in speed during a pumping portion of said cycle.18. The method of testing the test sample in liquid form for thermaloxidation stability as recited in claim 17 wherein said variable speedmotor turns an eccentric cam at different speeds that prolongs time ofsaid pumping portion but decreases time of said suction portion of saidcycle.
 19. The method of testing the test sample in liquid form forthermal oxidation stability as recited in claim 18 wherein said pumpingstep is with a single piston, positive displacement pump that includesan additional step of a measured flow rate of said test sample.
 20. Themethod of testing the test sample in liquid form for thermal oxidationstability as recited in claim 12 wherein fluctuations in said elevatedpressure are reduced by (a) having an eccentric cam turned by a motor ina pump to increase pumping time and decrease suction time, (b) varyingspeed of said motor to increase pumping time and decrease suction time,(c) dampening an output from said pump and (d) providing a high pressurerestriction downstream of said output.